Diagnostic methods for a high efficiency exhaust aftertreatment system

Abstract

An apparatus includes a nitrogen oxide (NOx) module and a selective catalytic reduction (SCR) diagnostic module. The NOx module is in exhaust gas communication with an exhaust flow of an exhaust aftertreatment system from an engine. The NOx module is structured to interpret NOx data indicative of an amount of NOx exiting the engine and an amount of NOx exiting the exhaust aftertreatment system, and determine a NOx conversion efficiency fault is present based on the amount of NOx exiting the engine and the amount of NOx exiting the exhaust aftertreatment system. The SCR diagnostic module is structured to determine at least one of a SCR catalyst and a diesel particulate filter including a coating of a SCR reaction catalyst (DPF-SCR) are responsible for the NOx conversion efficiency fault based on at least one of a reductant slip amount and a NOx conversion value across at least one of the SCR catalyst and the DPF-SCR.

What is claimed is: 
     
       1. An apparatus, comprising:
 an exhaust aftertreatment system in exhaust gas receiving communication with an engine, wherein the exhaust aftertreatment system includes a selective catalytic reduction (SCR) system, the SCR system including a SCR catalyst and a diesel particulate filter having a coating of a SCR reaction catalyst (DPF-SCR) positioned upstream of the SCR catalyst; 
 a nitrogen oxide (NOx) circuit in exhaust gas communication with an exhaust flow of the exhaust aftertreatment system from the engine, the NOx circuit structured to: 
 interpret NOx data indicative of an amount of NOx exiting the engine and an amount of NOx exiting the exhaust aftertreatment system; and 
 determine a NOx conversion efficiency fault is present based on the amount of NOx exiting the engine and the amount of NOx exiting the exhaust aftertreatment system; and 
 a selective catalytic reduction (SCR) diagnostic circuit structured to determine at least one of the SCR catalyst of the exhaust aftertreatment system and the DPF-SCR of the exhaust aftertreatment system are responsible for the NOx conversion efficiency fault based on at least one of a reductant slip amount and a NOx conversion value across at least one of the SCR catalyst and the DPF-SCR. 
 
     
     
       2. The apparatus of  claim 1 , wherein the SCR diagnostic circuit is structured to determine the DPF-SCR is faulty responsive to the reductant slip amount across the DPF-SCR being greater than an expected amount of reductant slip across the DPF-SCR. 
     
     
       3. The apparatus of  claim 2 , further comprising a reductant circuit structured to interpret reductant data to determine the reductant slip amount across the DPF-SCR based on an amount of reductant downstream of the DPF-SCR and an amount of reductant injected into the exhaust flow upstream of the DPF-SCR. 
     
     
       4. The apparatus of  claim 2 , wherein the SCR diagnostic circuit is structured to determine the expected amount of reductant slip across the DPF-SCR based on an expected amount of reductant downstream of the DPF-SCR and an amount of reductant injected into the exhaust flow upstream of the DPF-SCR, wherein the expected amount of reductant downstream of the DPF-SCR is based on at least one operating characteristic of the engine and the exhaust aftertreatment system. 
     
     
       5. The apparatus of  claim 1 , wherein the SCR diagnostic circuit is structured to determine at least one of (i) the SCR catalyst is faulty responsive to a difference between the NOx conversion value across the SCR catalyst and an expected NOx conversion value across the SCR catalyst being greater than or equal to a threshold value and (ii) the DPF-SCR catalyst is faulty responsive to the difference between the NOx conversion value across the SCR catalyst and the expected NOx conversion value across the SCR catalyst being less than the threshold value, wherein the SCR diagnostic circuit is further structured to verify that the DPF-SCR is faulty responsive to the reductant slip amount across the DPF-SCR being greater than an expected amount of reductant slip across the DPF-SCR. 
     
     
       6. The apparatus of  claim 5 , wherein the NOx circuit is structured to interpret the NOx data to determine the NOx conversion value across the SCR catalyst based on an actual amount of NOx in the exhaust flow downstream of the SCR catalyst and the amount of NOx exiting the engine when reductant is injected into the exhaust flow downstream of the DPF-SCR and upstream of the SCR catalyst. 
     
     
       7. The apparatus of  claim 5 , wherein the SCR diagnostic circuit is structured to determine the expected NOx conversion value across the SCR catalyst based on the amount of NOx exiting the engine and an expected amount of NOx in the exhaust flow downstream of the SCR catalyst when reductant is injected into the exhaust flow downstream of the DPF-SCR and upstream of the SCR catalyst, wherein the expected amount of NOx downstream of the SCR catalyst is based on at least one operating characteristic of at least one of the engine and the exhaust aftertreatment system. 
     
     
       8. The apparatus of  claim 7 , wherein the at least one operating characteristic of the engine includes at least one of an engine speed, an engine torque, and an exhaust flow characteristic, and wherein the at least one operating characteristic of the exhaust aftertreatment system includes at least one of a temperature of the exhaust flow, an amount of reductant injected into the exhaust flow, the amount of NOx exiting the engine, and the amount of NOx exiting the exhaust aftertreatment system. 
     
     
       9. The apparatus of  claim 1 , further comprising an engine circuit structured to provide at least one command to the engine to modulate the amount of NOx exiting the engine, wherein the at least one command includes actuating an exhaust throttle of an exhaust gas recirculation system in exhaust gas receiving communication with the engine to alter the exhaust flow through the SCR catalyst and affect the amount of NOx in the exhaust flow. 
     
     
       10. The apparatus of  claim 1 , further comprising a reductant circuit communicably coupled to a reductant dosing system and structured to control an amount and a location of injection of reductant into the exhaust flow. 
     
     
       11. A system, comprising:
 an exhaust aftertreatment system in exhaust gas receiving communication with an engine, wherein the exhaust aftertreatment system includes a selective catalytic reduction (SCR) system, the SCR system including a SCR catalyst and a diesel particulate filter having a coating of a SCR reaction catalyst (DPF-SCR) positioned upstream of the SCR catalyst; and 
 a controller communicably coupled to the engine and the exhaust aftertreatment system, the controller structured to: 
 receive first nitrogen oxide (NOx) data indicative of an amount of NOx in an exhaust flow exiting the engine and second NOx data indicative of an amount of NOx in the exhaust flow exiting the exhaust aftertreatment system; 
 determine a NOx conversion efficiency fault is present based on the first NOx data and the second NOx data; and 
 determine at least one of the SCR catalyst and the DPF-SCR of the SCR system are faulty responsive to the NOx conversion efficiency fault. 
 
     
     
       12. The system of  claim 11 , further comprising an exhaust throttle of an exhaust gas recirculation system positioned upstream of the SCR catalyst, wherein the controller is further structured to actuate the exhaust throttle to alter the exhaust flow through the SCR catalyst and affect the amount of NOx in the exhaust flow. 
     
     
       13. The system of  claim 11 ,
 wherein the exhaust aftertreatment system includes a first doser positioned upstream of the DPF-SCR, and a second doser positioned downstream of the DPF-SCR and upstream of the SCR catalyst; 
 wherein the first NOx data is provided by a first NOx sensor and the second NOx data is provided by a second NOx sensor; and 
 wherein the first NOx sensor and the second NOx sensor are structured as either one of or both of a physical sensor or a virtual sensor. 
 
     
     
       14. The system of  claim 13 , wherein the controller is further structured to:
 facilitate injection of reductant into the exhaust flow within the exhaust aftertreatment system downstream of the DPF-SCR and upstream of the SCR catalyst via the second doser; 
 acquire NOx data from the second NOx sensor indicative of an actual amount of NOx downstream of the SCR catalyst; 
 determine an expected amount of NOx downstream of the SCR catalyst based on operating characteristics of at least one of the engine and the exhaust aftertreatment system; and 
 determine the SCR catalyst is faulty responsive to a difference between the actual amount of NOx and the expected amount of NOx being greater than a threshold amount. 
 
     
     
       15. The system of  claim 13 , wherein the controller is further structured to:
 facilitate injection of reductant into the exhaust flow within the exhaust aftertreatment system upstream of the DPF-SCR via the first doser; 
 acquire reductant data from a reductant sensor indicative of an actual amount of reductant downstream of the DPF-SCR; 
 determine an expected amount of reductant downstream of the DPF-SCR based on operating characteristics of at least one of the engine and the exhaust aftertreatment system; and 
 determine the DPF-SCR is faulty responsive to the actual amount of reductant being greater than the expected amount of reductant.